Researchers of the Umeå University, in Sweden, carried out a study with 700,000 participants which shows that people who received the first dose of the covid-19 vaccine by Oxford / AstraZeneca and a second of messenger RNA They had greater protection against the coronavirus compared to those who received two doses of Oxford/AstraZeneca. The results were published in the journal The Lancet Regional Health – Europe.
The work shows “a greater reduction in the risk of infection for people who received an mRNA vaccine after they received a first dose of a vector-based vaccine compared to those who received the vector-based vaccine at both doses.” Peter Nordstrom, first author of the study.
Scientific evidence is quite clear to say that heterologous guidelines are much more immunogenic, safer and have better efficacy in preventing some symptoms
José Alcamí, virologist at the Carlos III Health Institute
The conclusions of this research are in agreement with those of the Spanish trial CombivacS in which the use of a second dose of Comirnaty vaccine (Pfizer / BioNtech) in people under 60 years of age already vaccinated with the first dose of Vaxzevria (Oxford / AstraZeneca).
Jose Alcamí, virologist of Carlos III Health Institute and Principal Investigator of CombivacS, notes in a reaction to the Swedish study, published in COVID-19 Vaccine Media Hub, that “the scientific evidence is amply clear to say that heterologous patterns are much more immunogenic, safer and, as this study shows, have a better efficiency in the prevention of some symptoms”.
Alcamí highlights that “all studies show that heterologous combination induces many more high quality antibodies, called neutralizers, compared to the counterparty, and that this pattern is secure”.
The work from Umeå University provides 50% efficacy against SARS-CoV-2 infection for the homologous double-dose combination of AstraZeneca. For the heterologous AstraZeneca / Pfizer, the efficiency is 67% and that of AstraZeneca / Moderna, 79%. “This is in line with what we know that Modern is a little more powerful than Pfizer”, emphasizes Alcamí.
A robust study
According to the expert, the heterologous combination is “significantly” better than the homologous with two doses of AstraZeneca. Also, the new study “is done with more than half a million people, so it’s robust,” he says.
In the survey, the group of peers who received AstraZeneca twice had an older average age of 67 years, compared with 44 years in the heterologous group. Alcamí indicates that he was worried “that there may be a certain prejudice, but when [el equipo] analyzed by confounding factors and covariance studies found that heterologous guidelines protect younger and older equally”.
Swedish research shows 50% efficacy against SARS-CoV-2 infection for the homologous double-dose combination of AstraZeneca. For the heterologous AstraZeneca / Pfizer, the efficiency is 67% and that of AstraZeneca / Moderna, 79%
On the contrary, the Spanish researcher continues, the homologous pattern protects the elderly more than the young. “When we say less protective, we mean mild or moderate symptoms. Both homologous and heterologous regimes offer enormous protection against hospitalization and death,” says Alcamí.
However, the scientist warns that the message that the homologous regimen is less effective must be modulated: “All combinations offer spectacular protection against hospitalization”, he points out. The Swedish university study looks at cases of mild symptoms, but the number of hospitalizations is very low, a few patients per group.
On the other hand, he clarifies, “the study is carried out in the Delta age and this shows that, although in the laboratory we see that the variant is blocked a little more by antibodies, in practice it doesn’t change much when it comes to avoiding severe cases”.
The Umeå University survey is based on data from the national registries of the Swedish Public Health Agency, the National Council for Health and Welfare and the Swedish Bureau of Statistics.
Marcel Ballin, co-author of the study, indicates that “the results of the study may have implications for vaccination strategies in different countries.”
Both homologous and heterologous regimens are highly protective against hospitalization and death
Jose Alcamí
“The World Health Organization has stated that despite the promising results of previous studies on the immune response of mixed vaccination, larger studies were needed to investigate its safety and efficacy in relation to clinical outcomes. Well, now we have one of these studies here”, concludes the researcher.
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